Bovine leukemia (malignant lymphoma, leukosis, lymphosarcoma) is a well characterized disease of cattle and sheep. See Theilen, et al, Veterinary Cancer Medicine, Lea and Febiger, Philadelphia, pp. 252-272, 1979; and Straub, A World Geography of Virus Diseases of Veterinary Importance, Section 2-B, Chapter 17, "Enzootic Bovine Leukosis", 1980. The causal agent is the bovine leukemia virus (BLV), first described by Miller, et al (J Natl Cancer Inst, 43:1297, 1969). Experimentally, BLV injections readily produce infection in susceptible bovine animals (Miller, et al, J Natl Cancer Inst, 48:423, 1972), although tumors (malignant lymphoma) rarely result. However, in sheep, BLV will produce malignant lymphomas within 8 to 18 months (Wittmann, et al, Arch Exp Veterinaermed, 23:709, 1969). BLV is genetically stable and has been found to be the same all over the world, that is, one virus strain is the causative agent and "mutants" do not seem to arise in nature. Becker, Y., Bovine Leukemia Virus--A Virologist's Point of View, In: Bovine Leucosis: Various Methods of Molecular Biology, pp. 435-443, Ed. by A. Burny, Published by the Commission of the European Communities, Luxembourg (1976).
In the world there is a population of approximately 11/4 billion cattle, and in the United States and other western developed countries about 250 million of which approximately half are beef and half dairy cattle (F.A.O. Bulletin, 1978). In the USA malignant lymphomas account for 60% of dairy cattle tumors and 10% of beef cattle which is similar in other parts of the world. The incidence rates of BLV infection varies considerably among beef and dairy cattle herds, but it is estimated that a high percentage of dairy cattle in the USA are infected with BLV which is true for most parts of the world. In herds where lymphosarcomas have a high frequency, BLV infection rates will reach 80 to 90% of all the adult cattle. It appears that the larger the herd, the greater the risk for tumorous malignant lymphomas (Sorenson, et al, Nord Vet Med Suppl I, 16:562, 1964).
Because of the great economic loss to cattlemen is most dairy producing countries, various European (EOC) nations are attempting to erradicate BLV by "test and slaughter". Purchase of cattle or semen from infected herds, is prohibited by law. Thousands of cattle that test positive are slaughtered every week in those EOC countries that participate in the "test and slaughter" program. See Straub, O.C., German Federal Research Institute for Animal Virus Diseases (Bundesforschungs Anstalt fur Viruskrankheiten der Tierre, Tubingen, West Germany). It cost the British government in 1978 about 41/2 million dollars in testing for BLV infection, and then paying an indemnity for 455 slaughtered cattle (Vet. Res., 104:401, 1979). Comparable or greater monetary losses occur in other EOC countries. Further, there is a controversy as to the justification of such "test and slaughter" programs, and over the accuracy of the testing methods.
A more efficient way to prevent the spread of BLV infection would be through the use of vaccines. This has been recognized and some attempts have been made to develop vaccines from inactivated BLV. See, for example, Miller, et al, Annales de Recherches Veterinaires, 9:871, 1978. There is an obvious need for an effective vaccine to protect cattle or sheep against BLV infection, and the lymphosarcoma and leukemia caused by such infection.